Landforms occur in patterns across the surface of the globe, and these landform complexes often define geographic or landscape regions. One way of looking at landforms is through elevation changes. A contour map is a useful two-dimensional representation of the surface and the most common way we have of symbolizing the relief of the surface. However, a type of map called a “shaded relief” map provides a more intuitive grasp of elevation.
Another way to understand landform regions or landscapes is to use a map that displays information about the geology. In the study of landforms, an understanding to the subsurface geology is critical. Understanding a geologic map requires a rough understanding of geologic time. A geologic map has the following properties:
- It recognizes similarities and differences among materials that make up the Earth’s crust and classifies them by type of rock or surficial deposit;
- It places Earth materials into a specific environment or origin- for example, a volcano, river deposit, windblown dune, limestone reef, alteration at depth by heat or pressure;
- It identifies rock formations of distinctive materials and ages that are the three-dimensional building blocks of the Earth’s crust; it further shows the relative position of one formation to another at the Earth’s surface;
- It arranges rock formations of different ages into a time sequence from which the geologic history of the planet can be deciphered.
For this lab we will address the following questions: Can we use a map of elevation (and rock age) to identify large-scale patterns in the landscape? What are the physiographic characteristics of North America?
Data and Methods:
You will need to:
- Download the maps
- Examine the maps in detail.
- Download and READ the materials that accompany the maps
- Thelin and Pike Relief Map http://pubs.usgs.gov/imap/i2206/i2206_pamphlet.pdf
- King and Beikman 1974 Relief Map http://pubs.usgs.gov/imap/i2720/i2720_pamphlet.pdf
- Finally (only after steps 1-3 are complete) Answer the questions. You will need to print an outline map to answer some of the questions. I have attached an outline map with this assignment. You may digitally edit the map instead of printing/scanning if you wish.
The shaded digital relief map by Thelin and Pike is a classic map displaying a wide variety of landforms. Thelin and Pike’s map uses digital elevation models to calculate the shadows that would fall across the landscape. It is interesting to note that research has shown that the human mind can most readily grasp the structure of the landscape when the digital sun is place in the Northwestern sky (a condition that cannot ever happen in most of North America!). The 1974 Geologic Map of the US by King and Beikman has been merged with the Elevation data in the Thelin and Pike map to form the geologic map we are using for this lab.
Along with the maps, descriptive documents are provided. These documents are extremely useful and several of the questions require you to read these documents.
Consider the following questions and answer them in your write up for this lab. You will need to use the maps AND the documentation to answer some of these questions (starting with question 3). You may use additional resources as necessary (e.g., for number 13 it might be helpful to google E-W trending mountain ranges).
- 1.Locate a geologic time scale and insert it into your lab report with a brief description. In terms of relative time, put these following geologic timeframes in order and indicate an approximate age for each (note: Some of these will overlap based on how they are classified): Holocene, Mississippian, Tertiary, Paleozoic, Pleistocene, Pennsylvanian, Mesozoic, Devonian, Triassic, Cambrian, Jurassic, Cretaceous
- 2.Where in your timeline is the K-T (or K-Pg) boundary? What happened here? (search the web if necessary).
- 3.Examine the overall map, characterize the large-scale patterns. East/West? North/South.
- For example, what trends do you see in the ‘relief’ of the map as you move across the country?
- 4.In general, where are the oldest rocks found?
- 5.Using the pamphlet, read the information on pages 5-15. On your outline map, identify areas described by numbers 7, 9, 12, 13, 16, 19, 22, 34, 35, 41, and 46?
- 6.How are folded ranges created?
- 7.Locate the Michigan Basin and the Nashville Dome, do the ages of the rocks have the same pattern in each feature (older-younger or younger to older?)
- 8.What is the geologic origin of Florida?
- 9.Explain how beach gravel deposits can be found in Lauderdale, Colbert, and Franklin County, Alabama.
- 10.From what period do the granite core of the black hills originate? How old are these rocks?
- 11.What are the “staked plains” and how did they get their name?
- 12.What is the cause of the “Basin and Range” province?
- 13.Most of the Mountain ranges trend N-S. Identify on your map the mountain ranges that trend E-W.
- 14.The Mississippi embayment is an area of flat land and very young sediments that show where the Gulf of Mexico filled in much of the lower Mississippi valley. On your map sketch and label the Mississippi embayment.
- 15.Crowley’s Ridge appears right through the heart of the Mississippi Embayment, label this feature and suggest how it might have been formed?
- 16.Glaciers covered much of North America as recently as 11,000 years ago. Can you identify landforms that are associated with the presence or melting of glacial ice? Identify on your map the extent of the most recent continental glaciation.
- 17.Locate the coastal barrier islands, what is the difference between east and west coasts? (Mexico is not an ocean!)
- 18.Sutter Buttes is plainly visible as a small but obvious ‘bump’ in the central valley of California. What sort of event would produce an isolated and singular ‘bump’ like this?